1. Field of the Invention
The present invention relates generally to reinforced flame retardant molding resin compositions. More particularly, this invention describes reinforced flame retardant polycarbodiimide modified copolyester molding resin compositions.
2. Summary of the Prior Art
Molding resin, such as glass reinforced polypropylene terephthalate and polybutylene terephthalate are flammable. The presence of many important reinforcing agents, such as glass, enhances rather than deters the burning rate of these molding resins. Since the reinforcing agents have a direct effect on the desirable physical-mechanical properties of these molding resins, several commercially advantageous applications may be precluded due to the flammability of these compositions.
U.S. Pat. No. 3,751,396, which is assigned to the assignee of the present invention, discloses that polypropylene terephthalate and polybutylene terephthalate molding resin compositions containing certain flame retardant additives disclosed in the prior art may have a tendency to drip flaming particles when subjected to a flame. An approach to overcome this deficiency has required the additional incorporation of a supplemental reinforcing agent, such as asbestos, having a length to diameter ratio greater than 50:1. However, the use of asbestos in particular is disadvantageous because of the health hazards which accompany the possible inhalation of asbestos fibers.
Furthermore, U.S. Pat. No. 3,794,617 discloses the preparation of flame retardant polyester fiber-forming compositions comprising the condensation product of a diol, a dicarboxylic acid, and a brominated diol of the formula ##STR1## wherein R is a bivalent hydrocarbon radical containing from 2 to 6 carbon atoms and n and m are integers from 1 to 10. The brominated diol is said to comprise 1 to 20 weight percent of the copolyester composition. It is not disclosed, however, that this particular fiber-forming polyester composition may be useful in molding resin applications.
It is also known to react carbodiimides with polyesters (see, e.g., U.S. Pat. Nos. 3,193,522; 3,193,523; 3,193,524 and 3,835,098). For example, U.S. Pat. No. 3,193,522 provides a process for stabilizing polyester compounds against hydrolytic degradation by employing highly substituted polycarbodiimide additives having molecular weights of at least about 500 and having more than three carbodiimide groups in a polycarbodiimide molecule. U.S. Pat. Nos. 3,193,523 and 3,193,524 disclose the use of monocarbodiimides to stabilize polyesters. Furthermore, U.S. Pat. No. 3,835,098 discloses the reaction of intermediate molecular weight thermoplastic elastomeric copolyesters with minor amounts of polycarbodiimide in order to provide compositions which exhibit properties similar to those exhibited by copolyesters having a higher degree of polymerization.
Copending U.S. patent application Ser. No. 715,946, filed Aug. 19, 1976 by N. W. Thomas, F. M. Berardinelli, and R. Edelman (continuation-in-part of U.S. Ser. No. 588,982, filed Mar. 7, 1975 -- now abandoned) which is assigned to the assignee of the present invention, generically discloses and claims a process for preparing certain polycarbodiimide modified thermoplastic polyesters. These modified thermoplastic polyesters have increased melt strength and are suitable for extrusion applications. This process comprises reacting the carboxyl end groups of a thermoplastic saturated polyester which is in the molten state with at least one polycarbodiimide which polycarbodiimide both (a) is derived from at least one aromatic diisocyanate which is either unsubstituted or contains up to one methyl substituent on each aromatic ring, and (b) contains at least three carbodiimide units per polycarbodiimide molecule.
The resulting polycarbodiimide modified thermoplastic polyesters have increased melt strength and intrinsic viscosity and a decreased number of carboxylic acid end groups. These improved melt strength polyesters also have improved die swell characteristics and are useful in extrusion applications such as blow molding.
Copending United States patent application Ser. No. 616,348, filed Sept. 24, 1975 (N. W. Thomas, F. M. Berardinelli and R. Edelman), is also assigned to the assignee of the present invention, discloses and claims an improved process for producing reinforced polycarbodiimide modified polyalkylene terephthalate molding resin compositions. This process comprises intimately mixing in the molten state a reinforcing agent with a polyalkylene terephthalate polymer such as polybutylene terephthalate or polypropylene terephthalate, the improvement in this process comprising
modifying the polyalkylene terephthalate polymer by reacting the polyalkylene terephthalate polymer in the molten state with at least one polycarbodiimide, which polycarbodiimide both
1. is derived from at least one aromatic diisocyanate which is either unsubstituted or contains up to one methyl substituent on each aromatic ring, and PA1 2. contains at least two carbodiimide units per polycarbodiimide molecule, whereby the resulting molding resin composition exhibits a substantially improved impact strength. PA1 1. a copolyester of PA1 2. at least one polycarbodiimide, which polycarbodiimide both
However, none of these patents or patent applications which disclose stabilizing or otherwise modifying polyesters by reacting them with carbodiimides disclose reinforced flame retardant compositions having non-drip characteristics.